This invention relates to bases for electric lamps and other threaded electrical connecting devices. More particularly, it concerns an improved base assembly for incandescent lamps by which the functional characteristics and aesthetic appearance of such bases is materially enhanced and also which contributes to reduced manufacturing costs as compared with those of lamp bases most commonly used at present.
Currently, bases for most commercially available incandescent electric lamps take the form of a threaded metal shell open at one end for receipt of the sealed glass envelope or bulb and having at its other end a glass insulator securing the assembly of one or more contact eyelets with the metal shell. The bases are manufactured as components for subsequent lamp-basing operations by placing the metal shell and eyelet(s) in a suitably contoured die, feeding a gob of molten glass into the die and molding the glass to a shape which encompasses portions of both the shell and the contact eyelet or eyelets if more than one is used.
Molding the glass insulator in situ is desirable from the standpoint of providing an integrated base structure but poses numerous problems, which though not apparent to the consuming public, are recognized as longstanding and essentially unsolved by the electric lamp industry. For example, the high temperatures at which the glass must be maintained for molding is undesirable in the base manufacturing operation both from the standpoint of high cost fuel consumption required to maintain the glass in a molten or moldable state and from the standpoint of deleterious effects on the metal components of the base. In this latter respect, heat transferred from the molten gob of glass weakens the metal by annealing to such an extent that shells are frequently deformed merely by required handling in transfer to lamp making machines. Also the heat discolors the metal so as to require chemical cleaning and brightening operations. In addition, imperfections in the molded glass insulators, such as voids resulting from an inadequate supply of glass or cracking and chipping of the glass either during molding or subsequent handling combine with the aforementioned difficulties to result in a high rejection rate either of the bases at the time of attachment to the lamp or of the lamps as a result of defective bases in the exercise of quality control.
Recognition of the problems associated with in situ molding of glass in the forming of lamp bases is evidenced in the prior patent art by U.S. Pat. No. 2,336,529 issued Dec. 14, 1943 to P. O. Cartun and U.S. Pat. No. 3,775,634 issued Nov. 27, 1973 to Richard F. Hasell et al as well as by the references cited in the texts of these patents. As further evidenced by the disclosures of these patents, solutions proposed heretofore have involved generally a redesign of the metal base shell to achieve a mechanical interlock between the shell and a preformed insulator. Also, the mechanical interconnection is predicated either by machined deformation of the metal shell or on elasticity of a shell portion in the nature of a spring clip or tang to retain the assembly of the insulator and the shell. It is believed that these alternative approaches to the use of in situ glass molding have been found unacceptable to the industry either because of costs or because of failure to achieve the required integration of base structure components. Irrespective of the reasons, the continued use of in situ glass molding of the lamp base insulator by the industry in spite of the recognized deficiencies with this manufacturing technique makes it clear that the alternatives represented by prior disclosures are less than completely satisfactory.